| 30 |Humaguaca | 21·415 | 57 | June 2 | 4 p.m.| | 8 |Cueba | 21·200 | 54 | 1 | | | 3 |Abra de Cortaderas | | | | | | 3 |Colorados | 19·350 | 50 | May 31 | 8 a.m.| | 6 |Cangrejos | 19·625 | 32 | 30 | 6 p.m.| | 9 |Quiaca | 19·300 | 50 | 29 | 4 p.m.| | 5 |Cumbre del Cerro} | 19·100 | 60 | 28 |11 a.m.| | | de Berque } | | | | | | 4 |Berque | 19·975 | 54 | 27 | 4 p.m.| | 5 |Talina | 20·800 | 56 | 26 | 9 a.m.| | 8 |Tupiza | 26·260 | 60 | 25 | 9 a.m.| +---------+---------------------+---------+-------+--------+-------+ _Note._--At Buenos Ayres the mean of the barometer for the month of March, 1822, was 29·61. In the upper parts of the Sierra de Cordova granite everywhere breaks through the surface, and innumerable fragments of it may be traced in the descent to the Travesia, whilst beyond that sandy zone there is not a vestige of it throughout the rest of the road to Potosi, the formation the whole way being of blue argillaceous schist and slate, with occasional strata of limestone and red sandstone. In the neighbourhood of Potosi, however, and on the tops of some of the highest mountains in its vicinity, Helms tells us that he fell in with a pretty thick stratum of granite pebbles rounded by the action of water. How, he says, could these masses of granite have been deposited here? Have they been rolled hither by a general deluge, or by some later partial revolution of nature? His astonishment would have been infinitely greater had he known that marine shells are to be found on the lofty mountain of Chorolque (about twelve leagues north-west from Tupiza, between Salta and Potosi), the summit of which has been determined by Dr. Redhead to be 16,530 feet above the level of the sea. The word Chorolque is corrupted from Churucolque, signifying in the Quichua tongue that the mountain contains silver and shells. The Spaniards, however, little suspected that the latter were to be found there, till, in 1826, an enterprising Frenchman ascended the mountain and brought down specimens which established beyond doubt the fact.